KEBAB STRUCTURES INDUCED BY SHISH BLOCKS OF ISOTACTIC POLYPROPYLENE
Shear-or flow-induced orientation of polymer chains, which is very common in polymer processing, has significant effects on the properties of polymer materials. The shish-kebab structure of polymer induced by a shear or flow field, which is one of the most important crystallization morphologies, has been studied for many years since it was reported firstly by Penning et al. in 1965.1 Over the past decades, many investigators have adopted the ideas of Keller and co-workers, who proposed the well accepted coilstretch transition theory.2 It is believed that the shish backbone is formed by the crystallization of fully extended polymer chains and the kebabs are folded chain lamellas that grow perpendicularly from the shish. However, the mechanism of shish formation is still a topic of ongoing debate. According to Kellers theory and other early views, only the length of chain is larger than a threshold chain length undergo the coil-stretch transition, leading to the formation of the shish backbone with fully stretched chains. Recently, simulation results indicated that the presence of coiled chains has a profound effect on the coil-stretch transition.3 It was found that not all the chains are fully extended in the shish due to the effects of coiled chains even at very high shear rates. It is clearly shown that the precursor structure contained the shish with the extended-chain conformation, which can be in anyone of amorphous,4 mesomorphic 5-7 or crystalline states1-3,8, according to in-situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) results. Kornfield et al. indicated that the long chains in an oriented melt recruit neighboring chains to join them in the formation of the shish based on the results of small-angle neutronscattering (SANS).910 The high-resolution scanning electron micrographs (SEM) and SAXS patterns of elongated polymer samples also revealed that the polymer chains in the shish backbone were neither fully stretched nor isolated. It is supposed that the competition between the relaxation and the nucleation of extended chains is responsible for the generation of the shish structure. The relation between the elongation and relaxation of chains on the formation of shish was shown by Yamazaki et al.11,12 They proposed that the shish is formed when the elongation of chains overcomes the conformational relaxation of the chains. However, it is difficult to observe the influence of the relaxation of the oriented chains on the formation of the shish structure in real space and in real time using SAXS, TEM, etc.
Jianiun Zhou Xi Jiang
Institute of Chemistry, Chinese Academy of Sciences, Beijing(100190), China College of Chemistry, Be Institute of Chemistry, Chinese Academy of Sciences, Beijing(100190), China
国际会议
PP’2010，Jinan International Symposium on Polymer Physics(2010济南国际高分子物理学术研讨会)
济南
英文
213-214
2010-06-06（万方平台首次上网日期，不代表论文的发表时间）